Method and device for assisting the pilot in controlling the turboshaft power and/or rotor speed of heat-propelled helicopters

ABSTRACT

Helicopter, device, and method of controlling helicopter using a computer, at least one motorized mechanical stop, and a collective pitch lever for controlling flight. The device includes a computer, a collective pitch lever, and at least one motorized mechanical stop controlled by the computer. The at least one motorized mechanical stop is adapted to obstruct the free movement of the collective pitch lever. The method includes detecting, using the computer, a deviation between a rotor speed limitation and a current speed, and actuating, using the computer, the at least one motorized mechanical stop. The at least one motorized mechanical stop is adapted to obstruct the free movement of the collective pitch lever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a device for assisting incontrolling, by acting on the collective pitch, the power transmitted tothe rotor(s) of helicopters by the engine or engines and thetransmission, and/or the rotor speed in autorotation. The invention alsorelates to heat-propelled helicopters equipped with such a device orusing such method.

2. Description of Background and Relevant Information

The driving of the rotors of heat-propelled helicopters requires a drivepower that must be precisely controlled, since this power varies orshould vary in accordance with various parameters (e.g., pilot demand,flight conditions, temperature, atmospheric pressure, etc.).

Moreover, there are limitations which must not be exceeded, withoutwhich the turboshaft engine(s) and/or the transmission could sustaindamages which are dangerous to the integrity of the helicopter. Theselimitations may be grouped into two categories:

mechanical limitations: wherein the maximum torque that the transmissioncan transmit without sustaining damage (for example, damage to thereduction gear located at the output of the drive shaft of theturboshaft engine);

thermal limitations, which are measured:

either by the maximum generating speed of the gas generator;

or by the maximum temperature of the gasses in the turbine or turbines.

The helicopter pilot must control the power transmitted to the rotor(s)by the turboshaft engine(s) and by the transmission by utilizing thecollective pitch in order to ensure that these limitations are notexceeded. To accomplish this, the pilot limits the upward movement ofthe collective pitch so as not to exceed the mechanical limitations ofthe transmission and the mechanical or thermal limitations of theturboshaft engine(s) indicated above.

In “Turbomeca” engines (Registered Trademark), the first thermallimitation reached is the maximum generating speed of the gas generator,and except in case of damage to the engine, the maximum temperature ofthe gasses is not reached until after that. Such an engine is said to beNg-controlled (also known as N1-controlled).

However, most foreign engines generally function in the opposite manner.Such engines are said to be “t4”-controlled or “t45”-controlled.

In order to observe the status of all of these limitations, the pilothas on the instrument panel several indicators, which can have multipleneedles. In all phases of the flight, the pilot must make sure that noneof these limits are exceeded. In the take-off and landing phases, inwhich it is additionally especially necessary to look outside thehelicopter, and in which the helicopter often experiences the limits ofits capabilities, this is a relatively difficult task which requires theconcentration of the pilot.

To make this task easier, retractable stops have been used in certainsingle-engine aircraft. For example, in “Gazelle” and “Dauphin” aircraft(Registered Trademarks), these stops are preset by the pilot as afunction of the exterior temperature.

Unfortunately, this type of stop can only protect the engine thermally,and only for a given type of flight: e.g., vertical flight is generallychosen for such protection. In essence, the power required by the rotorfor a given collective pitch depends on several parameters, i.e.,essentially on the atmospheric pressure, the exterior temperature andthe travel speed of the helicopter. However, this type of stop does notprotect the transmission from the harmful effects of excessive torque,at low altitude, and/or when the transmission is cold.

One object of the present invention is to overcome these drawbacks.

SUMMARY OF THE INVENTION

According to the invention, there is provided a method according towhich the approach and/or exceeding of a first limitation reached isdetected by a computer programmed to actuate a motorized mechanicalstop, producing the formation of a hard point countering thecontinuation of the upward pivoting movement of the collective pitchlever.

According to another characteristic of the invention, this method makesit possible to control the rotor speed of a helicopter in autorotation,and is remarkable in this application in that, upon detection of theapproach and/or exceeding of the desired rotor speed by way of acomputer programmed for this purpose, the computer is also programmed toactivate a motorized mechanical stop preset to a predetermined value ofthe collective pitch, in order to produce the formation of a hard pointor stop constituting an obstacle to the free continuation of thedownward pivoting movement of the collective pitch lever.

The invention also provides for a device for assisting the pilot incontrolling the power limitations of the turboshaft engine or engines ofheat-propelled helicopters. Such a device is remarkable in that itcomprises a motorized mechanical stop producing the formation of a hardpoint or stop countering the continuation of the upward pivotingmovement of the collective pitch lever, this motorized mechanical stopbeing activated by a computer programmed to detect the deviation betweenthe limitations and the corresponding power parameters, to select thegreatest one, and to actuate the stop as soon as any of the powerlimitations are reached or exceeded.

The device for assisting the pilot in controlling the rotor speed ofheat-propelled helicopters according to the invention is particularlyremarkable in that it comprises a motorized mechanical stop producingthe formation of a hard point or stop countering the continuation of thedownward pivoting movement of the collective pitch lever, this motorizedmechanical stop being activated by a computer programmed to detect thedeviation between the limitation of the rotor speed and the currentspeed, and to actuate the stop as soon as the maximum rotor speedsetting given to the computer is reached or exceeded.

According to another characteristic of the invention, theabove-mentioned method and device are also remarkable in that the hardpoint or stop created by the motorization actuated by the computer canbe bypassed through the action of a friction coupling placed between thestop or stops and the motorization, in order to allow the pilot tobypass this stop in case of emergency.

According to another characteristic of the invention, the motorizedmechanical stop system comprises an electric motor that drives anirreversible reduction gear linked to the collective pitch lever by wayof a linkage or transmission, and in that the electromechanical elementsof the motorized stop system are placed on an element of the linkage ortransmission, this element being constituted in two parts assembled withan ability to move relative to one another, one of these parts beingequipped with the stop or stops, while the other carries a stoppingdevice that can be brought into contact with the stop, or with any ofthe stops, which comprise(s) an electrical system for detecting contactwith the stopping device, the stop or stops preferably being adjustable.

From the preceding description, it is clear that the method and thedevice of the invention can use a system with a single motorizedmechanical stop, either to control the power limitations of theturboshaft engine or engines of the helicopter, or to control the rotorspeed of the engine.

However, a global solution offered by the invention provides for, in anespecially interesting way, creating two mechanical stops motorized bythe same motorization mechanism discussed above, and of subjecting themto the first limitation reached in the type of flying that thehelicopter is experiencing, and it is this highly advantageous solutionthat is described in the following description.

Thus, the pilot need only maintain a slight upward pressure on thecollective pitch lever to obtain the maximum allowable power. If thepilot releases this pressure and a power limitations is reached, thecontrol system will reduce the collective pitch so that this limitationsis not exceeded, but will not accordingly increase the power when it isreduced. It may be said that the pilot is the motoroperator of thiscontrol system, which allows him at any time, and without looking at hisinstruments, i.e., inside, to avoid exceeding the limitations whileremaining in the “control loop”.

The same device, when the computer receives the rotor speed, can assistin controlling the rotor speed in autorotation. In essence, the lowercollective pitch stop must be set so as to provide enough rotor speed inautorotation at its minimum mass, for the low altitude and the minimumtemperature at which it is rated. Conversely, when the aircraft is full,if it is flying high and it is hot, and/or if the pilot maintains thepitch at the lower stop, the maximum allowable rotor speed can be easilyexceeded. With the method and the device according to the invention, thepilot need only maintain a slight downward pressure on the collectivepitch in order to obtain the maximum speed setting that has been givento the computer.

Of course, in any case, a spring or friction device will allow the pilotto bypass this stop in case of emergency.

According to another aspect of the invention, there is provided a methodfor assisting in controlling at least one power limitation of ahelicopter using a computer, at least one motorized mechanical stop, anda collective pitch lever for controlling flight, the method comprisingdetecting, using the computer, a deviation between the at least onepower limitation and at least one corresponding power parameter,selecting, using the computer, a greater one of the at least one powerlimitation and the at least one power parameter, and actuating, usingthe computer, the at least one motorized mechanical stop, wherein the atleast one motorized mechanical stop is adapted to obstruct the freemovement of the collective pitch lever. The at least one motorizedmechanical stop may be adapted to counter a free continuation of anupward pivoting movement of the collective pitch lever as soon as the atleast one power limitation is reached or exceeded. The at least onepower limitation may comprise one of a power limitation of atransmission of the helicopter or a power limitation of at least oneturboshaft engine of the helicopter. The method may further comprisebypassing the at least one motorized mechanical stop. The method mayfurther comprise bypassing, in an emergency, the at least one motorizedmechanical stop using one of a mechanism and a friction coupling.

The invention also provides for a method for controlling a rotor speedof a helicopter in autorotation, the helicopter including flightcontrols which comprise a computer, at least one motorized mechanicalstop, and a collective pitch lever for controlling flight, the methodcomprising detecting, using the computer, a deviation between a rotorspeed limitation and a current speed, and actuating, using the computer,the at least one motorized mechanical stop, wherein the at least onemotorized mechanical stop is adapted to obstruct the free movement ofthe collective pitch lever. The method may further comprise inputtinginto the computer a maximum rotor speed setting, wherein the at leastone motorized mechanical stop is adapted to counter a free continuationof a downward pivoting movement of the collective pitch lever as soon asthe maximum rotor speed setting is reached or exceeded. The method mayfarther comprise bypassing the at least one motorized mechanical stop.The method may further comprise bypassing, in an emergency, the at leastone motorized mechanical stop using one of a mechanism and a frictioncoupling.

The invention also contemplates a device for assisting in controlling atleast one power limitation of at least one turboshaft engine of ahelicopter, the device comprising a computer, a collective pitch lever,and at least one motorized mechanical stop controlled by the computer,wherein the at least one motorized mechanical stop is adapted toobstruct the free movement of the collective pitch lever. The at leastone motorized mechanical stop may be adapted to counter a freecontinuation of an upward pivoting movement of the collective pitchlever. The computer may be programmed to detect a deviation between theat least one power limitation and at least one corresponding powerparameter. The computer may be adapted to select a greater one of the atleast one power limitation and the at least one power parameter. Thecomputer may be adapted to actuate the at least one motorized mechanicalstop as soon as the at least one power limitation is reached orexceeded. The device may further comprise a mechanism for bypassing theat least one motorized mechanical stop. The device may further comprisea friction coupling for bypassing, in an emergency, the at least onemotorized mechanical stop. The at least one motorized mechanical stopmay be part of a motorized mechanical stop system which includes anelectric motor, an irreversible reduction gear, at least twoelectromechanical elements, and a movable element which is adapted tocontact each of the at least two electromechanical elements. Themotorized mechanical stop system may further include a first shaftcoupling the reduction gear to the movable element and a second shaftcoupling the movable element to a collective pitch linkage. Themotorized mechanical stop system may further include a plate upon whichis mounted the at least two electromechanical elements, and wherein themovable element is mounted to the second shaft. The motorized mechanicalstop system may further include a plate upon which is mounted the atleast two electromechanical elements. The motorized mechanical stopsystem may further include an electrical system for detecting contactbetween the at least two electromechanical elements and the movableelement. A position of the at least two electromechanical elements maybe adjustable. The device may further comprise a friction couplingdisposed between the first and second shafts. The device may furthercomprise a friction coupling disposed between an irreversible reductiongear and at least one of the movable element or the at least twoelectromechanical elements. The motorized mechanical stop system mayfurther include a safety device disposed between the movable element anda lever which is coupled to a collective pitch linkage, the safetydevice preventing a mechanical locking.

According to another embodiment, the invention provides for a device forassisting in controlling a rotor speed of a helicopter in autorotation,the device comprising a computer, a collective pitch lever, and at leastone motorized mechanical stop controlled by the computer, wherein the atleast one motorized mechanical stop is adapted to obstruct the freemovement of the collective pitch lever. The at least one motorizedmechanical stop may be adapted to counter a free continuation of adownward pivoting movement of the collective pitch lever. The computermay be programmed to detect a deviation between a rotor speed limitationand a current speed. The computer may be programmed with a maximum rotorspeed setting and wherein the computer is adapted to actuate the atleast one motorized mechanical stop as soon as the maximum rotor speedsetting is reached. The device may further comprise a mechanism forbypassing the at least one motorized mechanical stop. The device mayfurther comprise a friction coupling for bypassing, in an emergency, theat least one motorized mechanical stop. The at least one motorizedmechanical stop may be part of a motorized mechanical stop system whichincludes an electric motor, an irreversible reduction gear, at least twoelectromechanical elements, and a movable element which is adapted tocontact each of the at least two electromechanical elements. Themotorized mechanical stop system may further include a first shaftcoupling the reduction gear to the movable element and a second shaftcoupling the movable element to a collective pitch linkage. Themotorized mechanical stop system may further include a plate upon whichis mounted the at least two electromechanical elements, and wherein themovable element is mounted to the second shaft. The motorized mechanicalstop system may further include a plate upon which is mounted the atleast two electromechanical elements. The motorized mechanical stopsystem may further include an electrical system for detecting contactbetween the at least two electromechanical elements and the movableelement. A position of the at least two electromechanical elements maybe adjustable. The device may further comprise a friction couplingdisposed between the first and second shafts. The device may furthercomprise a friction coupling disposed between an irreversible reductiongear and at least one of the movable element or the at least twoelectromechanical elements. The motorized mechanical stop system mayfurther include a safety device disposed between the movable element anda lever which is coupled to a collective pitch linkage, the safetydevice preventing a mechanical locking.

The invention further provides for a heat-propelled helicopter having asystem for assisting in controlling at least one power limitation of ahelicopter using a computer, a motorized mechanical stop system havingat least one motorized mechanical stop, and a collective pitch lever forcontrolling flight, the system being adapted to detect, using thecomputer, a deviation between the at least one power limitation and atleast one corresponding power parameter, to select, using the computer,a greater one of the at least one power limitation and the at least onepower parameter, and to actuate, using the computer, at least onemotorized mechanical stop, wherein the at least one motorized mechanicalstop is adapted to obstruct the free movement of the collective pitchlever.

Additionally, the invention provides for a heat-propelled helicopterhaving a system for controlling a rotor speed of a helicopter inautorotation, the helicopter including flight controls which comprise acomputer, a motorized mechanical stop system having at least onemotorized mechanical stop, and a collective pitch lever for controllingflight, the system being adapted to detect, using the computer, adeviation between a rotor speed limitation and a current speed, and toactuate, using the computer, the at least one motorized mechanical stop,wherein the at least one motorized mechanical stop is adapted toobstruct the free movement of the collective pitch lever.

A heat-propelled helicopter is also provided which has a system forassisting in controlling at least one power limitation of at least oneturboshaft engine of a helicopter, the system comprising a computer, acollective pitch lever, and a motorized mechanical stop system having atleast one motorized mechanical stop controlled by the computer, whereinthe at least one motorized mechanical stop is adapted to obstruct thefree movement of the collective pitch lever.

The invention still further provides for a heat-propelled helicopterhaving a system for assisting in controlling a rotor speed of ahelicopter in autorotation, the system comprising a computer, acollective pitch lever, and a motorized mechanical stop system having atleast one motorized mechanical stop controlled by the computer, whereinthe at least one motorized mechanical stop is adapted to obstruct thefree movement of the collective pitch lever.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object,characteristics and advantages, and still others, willemerge more clearly from the following description and the attacheddrawings, in which:

FIG. 1 is a schematic view illustrating the installation of themotorized mechanical stop in the collective pitch control.

FIG. 2 is a schematic representation of a first exemplary embodiment ofthe motorized mechanical stop device according to the invention.

FIG. 3 is a schematic representation of a variant of embodiment of thismotorized mechanical stop device.

FIG. 4 is a schematic detail on a larger scale of the electromechanicalcomponents of this variant of embodiment of the motorized mechanicalstop device.

FIG. 5 represents the graph of the curves illustrating the relationshipbetween the collective pitch and the reduced power input.

FIGS. 6 and 6a represent these same curves for stationary flight atstandard pressure (1013 hPa).

FIG. 7 represents the functional diagram of the control system of thestop at the power limitation, in flight with engine drive.

FIG. 8 is a functional diagram of the control system of the stop at thelimitation in autorotation.

DETAILED DESCRIPTION OF THE INVENTION

The drawings will be referred to in order to describe some advantageous,though non-limiting, exemplary embodiments of the motorized mechanicalstop device according to the invention.

The installation of this device in the flight controls is schematicallyrepresented in FIG. 1. The motorized mechanical stop system, designatedoverall by reference 1, is disposed so that its output lever 14 isconnected, by a connecting rod 15 to the collective pitch linkage 4 a,upstream from a mixing unit or collective/pitch synchronizer 4. Acollective pitch lever 3 is itself connected, in the conventional way,by a connecting rod 20, to the synchronizer 4, which comprises thecollective pitch linkage 4 a and cyclic pitch linkage 4 b which controlsand is itself connected to the servocontrols 5 in contact with the swashplate 6 of the rotor 7 of the aircraft (only a cyclic control and aservocontrol are schematically represented, in order not tounnecessarily over complicate the drawing). The motorized mechanicalstop system is electrically connected to the computer 2.

A first possible exemplary assembly is represented in FIG. 2. Accordingto this embodiment, the motorized mechanical stop system according tothe invention comprises an electric servocontrol 10 controlled by thecomputer 2 of the helicopter and an irreversible reduction gearbox 11whose output is connected to one of the ends of a shaft 13A, by afriction coupling 12. The opposite end of the shaft 13A is subject tothe two upper and lower stops 17A, 17B. Each of these stops 17A, 17Bcomprises a contact system 17′, 17′, which respectively makes itpossible to detect when a stopping device 16 integral with a shaft 13Bcomes into contact with either of them. This shaft 13B is disposed inthe extension of the shaft 13A, to which it is linked by a coupling thatallows them to move relative to one another. The opposite end of theshaft 13B is integral with one of the ends of the pivoting lever 14, theother end of which is connected, via a rigid jointed connecting rod 15,to the collective pitch linkage 4 a.

The linkage between the shaft 13B and the collective pitch lever 3 issuch that any pivoting movement of the latter results in a rotation ofcorresponding amplitude of the shaft 13B.

The position of the stops 17A, 17B, on which the electrical contacts aremounted, is adjustable in accordance with the characteristics of thetype of helicopter in which the device of the invention is installed.

The contacts 17A′, 17B′ of the stops 17A, 17B are electrically connectedto the computer 2.

Conventionally, in the remainder of the present description, the stop17A is considered to be the upper stop (power limitation), while thestop 17B is the lower stop (NR limitation).

The control device according to the invention also comprises:

a safety device 18 mounted on the connector of the pivoting lever 14 andadapted to prevent any mechanical locking of the device (this safetydevice can be constituted by a pin that is breakable under a certainmoment, for example, when a pressure of force greater than about ten kgis applied to the end of the collective stick and/or collective pitchlever 3),

a device 19 for copying the position of the stops.

FIGS. 3 and 4 illustrate a variant of embodiment of the motorizedmechanical stop system according to the invention.

In this variant (FIG. 3), the motorized mechanical stop system alsocomprises an electric servocontrol engine 10 controlled by the computer2 and an irreversible reduction gearbox 11 whose output is linked to oneof the ends of a shaft 13, by a friction coupling 12. The opposite endof the shaft 13 is integral with the lever 14, which is connected by aconnecting rod 15, to the collective pitch linkage 4 a. This variantdiffers from the embodiment described above by the fact that theelectromechanical components of the stops are incorporated into theconnecting rod 15 connecting the pivoting lever 14 and the collectivepitch lever 3.

In this case, the connecting rod 15 that incorporates the two stops(upper and lower) is primarily constituted in two parts 15 a, 15 bassembled with an ability to move axially relative to one another. Thepart 15 a is constituted by a rod, for example, cylindrical, comprisingan external end equipped with an eye end 15 c connected to the pivotinglever 14, and an opposing internal portion 15 d housed with an abilityto slide inside the part 15 b. The internal portion 15 d is equippedwith a stopping device 16 that can move between two stops 17A, 17B,whose sides disposed facing one another carry, respectively, theelectrical contacts 17A′, 17B′ (not represented). The stop 17B can beconstituted by a threaded bush comprising an axial opening for thepassage of the rod 15 a and an external threading that allows it to bescrewed into an internal threading 15 e of the internal lateral wall ofa cylindrical recess 15 f of one of the end portions of the part 15 b.The second stop 17A is constituted by the bottom of the recess 15 f inwhich the stopping device 16 and the bush 17B are housed. It isunderstood that the embodiment of the stop 17B in the form of a threadedbush allows the position of the latter to be adjusted.

The part 15 b of the connecting rod 15 that is connected to thecollective pitch lever by an eye end 15 g is itself embodied in twoparts 15 b′, 15 b″ assembled by screwing, i.e., each part 15 b′ and 15b″ has threads which engage each other, so as to allow the position ofthe stop 17A to be adjusted.

In a helicopter, determining the limit pitch that gives the maximumallowable power is complicated; in fact, it depends on severalparameters:

air speed;

altitude;

temperature.

Directly determining this limit pitch for each helicopter would requireextremely accurate, hence costly, sensors, and a specific calibration ofeach apparatus; since all helicopters of the same type are not strictlyidentical, this would not be an economically realistic solution.

A simpler solution provides for approximately presetting the stop forthe most critical type of flight (stationary flight at sea level understandard conditions for the take-off limitations, and climbing under thesame conditions for the maximum continuous power limitation) and thenleaving it up to the control system to set the stop to the correct valuequickly enough not to exceed the acceptable transitory limits on thepower levels. It is this solution that is proposed here; i.e., itrequires only one speed sensor that operates in an all-or-nothing way ataround 55 kt, generally already available in the helicopter. If thissolution did not prove fast enough, the stop could then be preset as afunction of the exterior temperature, in accordance with the curves ofFIGS. 6 and 6a, and this would require the presence of an exteriortemperature sensor.

The operating principle is the same in autorotation: the stop can alsobe preset to a fixed value (e.g., determined by in-flight tests); assoon as the rotor speed reaches the speed setting or the pitch comesinto contact with the lower stop (i.e., contact 17B closed), the controlsystem is activated and maintains the rotor speed setting as long as thepilot exerts downward pressure on the collective pitch lever 3.

Upper Stop (Power Limitation)

The stop 17A will be preset as indicated above. The control system willonly be rendered operational under three conditions:

when a limitation is reached or exceeded;

when the stop is reached (i.e., closing of the contact 17A′ of the stop17A);

when, in a fast maneuver of the collective pitch, the power limitationis near. For this reason, it is necessary to enter dC/dt, DNg/dt anddt4/dt terms into the computer in order to adjust the preset stop valuedownward and provide the appropriate choking.

This means that the preset value of the stop will only be modified whenone of the three above conditions is fulfilled; if it is modified, thislatter position will be saved in memory as long as the device is notreactivated by at least one of the three above conditions.

Lower Stop (NR Limitation)

The fixed value set depends on the helicopter. This preset value must beoperative for flight in autorotation, i.e., when the rotor speed isgreater than the maximum controlled speed. Here again, in order to coverfast maneuvers and provide the necessary choking, a dNR/dt term will benecessary in order to adjust the position of the stop upward.

Operation of the Control System

It will be recalled that the control system of the stop at thelimitation is activated as soon as one of the stops or a limitation isapproached too quickly (torque, Ng, t4, or NR).

Under Power

The computer determines the power limitation to be taken into account:

Vi < 55 kt 5 minute limitation Vi > 55 kt maximum continuous limitationengine failure emergency limitation

It then calculates the deviations between the current values and thecorresponding limitations (torque, Ng, t4), selects the greatestdeviation and sends it to the control system of the engine, associatingwith it a derived term and an integrated term in order to actuate thedisplacement of the stop 17A. Thus, the limitation taken into account isthe first one reached, and it remains active as long as none of theothers exceeds its limit and replaces it, or as long as the contact 17A′of the stop 17A remains closed. The functional diagram of this operationis represented in FIG. 7.

In Autorotation

The diagram is similar and represented in FIG. 8.

What is claimed is:
 1. A method for assisting in controlling at leastone power limitation of a helicopter using a computer, at least onemotorized mechanical stop, and a collective pitch lever for controllingflight, the method comprising: detecting, using the computer, adeviation between the at least one power limitation and at least onecorresponding power parameter; selecting, using the computer, a greaterone of the at least one power limitation and the at least one powerparameter; and actuating, using the computer, the at least one motorizedmechanical stop, wherein the at least one motorized mechanical stop isadapted to obstruct the free movement of the collective pitch lever. 2.The method of claim 1, wherein the at least one motorized mechanicalstop is adapted to counter a free continuation of an upward pivotingmovement of the collective pitch lever as soon as the at least one powerlimitation is reached or exceeded.
 3. The method of claim 1, wherein theat least one power limitation comprises one of a power limitation of atransmission of the helicopter or a power limitation of at least oneturboshaft engine of the helicopter.
 4. The method of claim 1, furthercomprising bypassing the at least one motorized mechanical stop.
 5. Themethod of claim 1, further comprising bypassing, in an emergency, the atleast one motorized mechanical stop using one of a mechanism and afriction coupling.
 6. A method for controlling a rotor speed of ahelicopter in autorotation, the helicopter including flight controlswhich comprise a computer, at least one motorized mechanical stop, and acollective pitch lever for controlling flight, the method comprising:detecting, using the computer, a deviation between a rotor speedlimitation and a current speed; and actuating, using the computer, theat least one motorized mechanical stop, wherein the at least onemotorized mechanical stop is adapted to obstruct the free movement ofthe collective pitch lever.
 7. The method of claim 6, furthercomprising: inputting into the computer a maximum rotor speed setting,wherein the at least one motorized mechanical stop is adapted to countera free continuation of a downward pivoting movement of the collectivepitch lever as soon as the maximum rotor speed setting is reached orexceeded.
 8. The method of claim 6, further comprising bypassing the atleast one motorized mechanical stop.
 9. The method of claim 6, furthercomprising bypassing, in an emergency, the at least one motorizedmechanical stop using one of a mechanism and a friction coupling.
 10. Adevice for assisting in controlling at least one power limitation of atleast one turboshaft engine of a helicopter, the device comprising: acomputer; a collective pitch lever; and at least one motorizedmechanical stop controlled by the computer, wherein the at least onemotorized mechanical stop is adapted to obstruct the free movement ofthe collective pitch lever.
 11. The device of claim 10, wherein the atleast one motorized mechanical stop is adapted to counter a freecontinuation of an upward pivoting movement of the collective pitchlever.
 12. The device of claim 10, wherein the computer is programmed todetect a deviation between the at least one power limitation and atleast one corresponding power parameter.
 13. The device of claim 12,wherein the computer is adapted to select a greater one of the at leastone power limitation and the at least one power parameter.
 14. Thedevice of claim 13, wherein the computer is adapted to actuate the atleast one motorized mechanical stop as soon as the at least one powerlimitation is reached or exceeded.
 15. The device of claim 10, furthercomprising a mechanism for bypassing the at least one motorizedmechanical stop.
 16. The device of claim 10, further comprising afriction coupling for bypassing, in an emergency, the at least onemotorized mechanical stop.
 17. A device for assisting in controlling atleast one power limitation of at least one turboshaft engine of ahelicopter, the device comprising: a computer; a collective pitch lever;and at least one motorized mechanical stop controlled by the computer,wherein the at least one motorized mechanical stop is adapted toobstruct the free movement of the collective pitch lever, and whereinthe at least one motorized mechanical stop is part of a motorizedmechanical stop system which includes an electric motor, an irreversiblereduction gear, at least two electromechanical elements, and a movableelement which is adapted to contact each of the at least twoelectromechanical elements.
 18. The device of claim 17, wherein themotorized mechanical stop system further includes a first shaft couplingthe reduction gear to the movable element and a second shaft couplingthe movable element to a collective pitch linkage.
 19. The device ofclaim 18, wherein the motorized mechanical stop system further includesa plate upon which is mounted the at least two electromechanicalelements, and wherein the movable element is mounted to the secondshaft.
 20. The device of claim 17, wherein the motorized mechanical stopsystem further includes a plate upon which is mounted the at least twoelectromechanical elements.
 21. The device of claim 17, wherein themotorized mechanical stop system further includes an electrical systemfor detecting contact between the at least two electromechanicalelements and the movable element.
 22. The device of claim 17, wherein aposition of the at least two electromechanical elements is adjustable.23. The device of claim 18, further comprising a friction couplingdisposed between the first and second shafts.
 24. The device of claim18, further comprising a friction coupling disposed between anirreversible reduction gear and at least one of the movable element orthe at least two electromechanical elements.
 25. The device of claim 18,wherein the motorized mechanical stop system further includes a safetydevice disposed between the movable element and a lever which is coupledto a collective pitch linkage, the safety device preventing a mechanicallocking.
 26. A device for assisting in controlling a rotor speed of ahelicopter in autorotation, the device comprising: a computer; acollective pitch lever; and at least one motorized mechanical stopcontrolled by the computer, wherein the at least one motorizedmechanical stop is adapted to obstruct the free movement of thecollective pitch lever.
 27. The device of claim 26, wherein the at leastone motorized mechanical stop is adapted to counter a free continuationof a downward pivoting movement of the collective pitch lever.
 28. Thedevice of claim 26, wherein the computer is programmed to detect adeviation between a rotor speed limitation and a current speed.
 29. Thedevice of claim 28, wherein the computer is programmed with a maximumrotor speed setting and wherein the computer is adapted to actuate theat least one motorized mechanical stop as soon as the maximum rotorspeed setting is reached.
 30. The device of claim 26, further comprisinga mechanism for bypassing the at least one motorized mechanical stop.31. The device of claim 26, further comprising a friction coupling forbypassing, in an emergency, the at least one motorized mechanical stop.32. A device for assisting in controlling a rotor speed of a helicopterin autorotation, the device comprising: a computer; a collective pitchlever; and at least one motorized mechanical stop controlled by thecomputer, wherein the at least one motorized mechanical stop is adaptedto obstruct the free movement of the collective pitch lever, and whereinthe at least one motorized mechanical stop is part of a motorizedmechanical stop system which includes an electric motor, an irreversiblereduction gear, at least two electromechanical elements, and a movableelement which is adapted to contact each of the at least twoelectromechanical elements.
 33. The device of claim 32, wherein themotorized mechanical stop system further includes a first shaft couplingthe reduction gear to the movable element and a second shaft couplingthe movable element to a collective pitch linkage.
 34. The device ofclaim 33, wherein the motorized mechanical stop system further includesa plate upon which is mounted the at least two electromechanicalelements, and wherein the movable element is mounted to the secondshaft.
 35. The device of claim 32, wherein the motorized mechanical stopsystem further includes a plate upon which is mounted the at least twoelectromechanical elements.
 36. The device of claim 32, wherein themotorized mechanical stop system further includes an electrical systemfor detecting contact between the at least two electromechanicalelements and the movable element.
 37. The device of claim 32, wherein aposition of the at least two electromechanical elements is adjustable.38. The device of claim 33, further comprising a friction couplingdisposed between the first and second shafts.
 39. The device of claim32, further comprising a friction coupling disposed between anirreversible reduction gear and at least one of the movable element orthe at least two electromechanical elements.
 40. A device for assistingin controlling a rotor speed of a helicopter in autorotation, the devicecomprising: a computer; a collective pitch lever; and at least onemotorized mechanical stop controlled by the computer, wherein the atleast one motorized mechanical stop is adapted to obstruct the freemovement of the collective pitch lever, and wherein the motorizedmechanical stop system further includes a safety device disposed betweenthe movable element and a lever which is coupled to a collective pitchlinkage, the safety device preventing a mechanical locking.
 41. Aheat-propelled helicopter having a system for assisting in controllingat least one power limitation of a helicopter using a computer, amotorized mechanical stop system having at least one motorizedmechanical stop, and a collective pitch lever for controlling flight,the system being adapted to detect, using the computer, a deviationbetween the at least one power limitation and at least one correspondingpower parameter, to select, using the computer, a greater one of the atleast one power limitation and the at least one power parameter, and toactuate, using the computer, at least one motorized mechanical stop,wherein the at least one motorized mechanical stop is adapted toobstruct the free movement of the collective pitch lever.
 42. Aheat-propelled helicopter having a system for controlling a rotor speedof a helicopter in autorotation, the helicopter including flightcontrols which comprise a computer, a motorized mechanical stop systemhaving at least one motorized mechanical stop, and a collective pitchlever for controlling flight, the system being adapted to detect, usingthe computer, a deviation between a rotor speed limitation and a currentspeed, and to actuate, using the computer, the at least one motorizedmechanical stop, wherein the at least one motorized mechanical stop isadapted to obstruct the free movement of the collective pitch lever. 43.A heat-propelled helicopter having a system for assisting in controllingat least one power limitation of at least one turboshaft engine of ahelicopter, the system comprising a computer, a collective pitch lever,and a motorized mechanical stop system having at least one motorizedmechanical stop controlled by the computer, wherein the at least onemotorized mechanical stop is adapted to obstruct the free movement ofthe collective pitch lever.
 44. A heat-propelled helicopter having asystem for assisting in controlling a rotor speed of a helicopter inautorotation, the system comprising a computer, a collective pitchlever, and a motorized mechanical stop system having at least onemotorized mechanical stop controlled by the computer, wherein the atleast one motorized mechanical stop is adapted to obstruct the freemovement of the collective pitch lever.